Method of treating metal articles



Patented Feb. 10, 1925. I

UNITED STATES PATENT OFFICE.

WILLIAM H. GRAVES, JR., OF DETR OIT, MICHIGAN, ASSIGNOR TO PACKARD MOTORCAR COMPANY, 015 DETROIT, MICHIGAN, ACORPQRATION OF MICHIGAN.

METHOD OF TREATING METAL ARTICLES.

No Drawing.

To all whom it may. concern-.-

Be it known that I, WILLIAM H. GRAVES, J12, a citizen of the UnitedStates, and resident of Detroit, WVayne County, State of Michigan, haveinvented certain new and useful Improvements in Methods of TreatingMetalvArticlcs, of which the following is a specification.

This invention or discovery relates to the treatment of metal articlesand it is particularly directed to the cleaning and removal of scalefrom hardened steel articles such as gears without injuring the articlesor materially changing the physical properties thereof.

The invention or discovery will be described in connection with thetreatment of hardenedsteel gears such as are used in the transmission orgear box of an automobile, though it is, of course, applicable to othergears and to other metal articles.

In the manufacture of steel gears for such uses as suggested above, thegears are, after being cut, hardened by heating to a temperature ofaround 1500 F. and then quenched in liquid such as oil. This operationproduces a scale on the surface ofthe articles and they are unfit foruse until such scale has been removed and the surface of the gear,particularly the teeth, is left clean. The scale is a hard abrasivesubstance which would soon wear bearing surfaces and would, therefore,quickly destroy the gears if they were used without having the scaleremoved from them.

In usual practice the scale is removed by the use of rapidly Evolvingwire brushes and in some cases by a file or' the scraping action of ahard instrument. This requires considerable time and the brushes wearrapidly so that this method is expensive. This is also a difficultmethod where the gear or article has small teeth or interstices or whereteeth or key-ways are cut inside of the gear hub.

Attempts have been made to clean such gears or remove the scaletherefrom by the use of an electricallv operated acid bath but it hasbeen found that subjecting a hardened gear to such bath greatly changesthe physical properties of the material as by reducing its strength orductility and such cleaning operations have not, therefore, been foundpracticable where maximum strength of material is important.

Application filed June 10, 1922. semi No. 567,432.

from which the hardening strains have not been removed, it results ingreatly reducing the strength of the hardened gear and while drawing thetemper thereafter restores the strength somewhat yet the gear is stillfar from its original strength. The present invention or discoverypermits the use of an electrically operated acid bath in removing thescale from hardened gears without materially changing the physicalproperties of the metal.

The present invention or discovery consists principally of somewhatdrawing the temper from the hardened steel articl'esbefore subjectingthem to the acid bath and thus the strains in the metal are removedbefore the acid is permitted to act upon the articles. Morespecifically, the invention or discovery may be described as follows:The metal artieleis heated to a suitable temperature above its criticalpoint, say 1500 F., and quenched in oil, thus hardening it. Sometimesthis hardening step is repeated by a second heating and quenching. Thishardening operation leaves a scale on the gear or article and it is thenheated again, preferably to a lesser degree than in the hardeningoperation, say 7009 F., so that a part of the temper is drawn from thegear. The gear is then cooled. Some of the scale still remains on thegear and it is then subjected to an acid cleaning operation. This acidcleaning operation, in full, preferably consists of, first, washing thegears in an alkaline solution to clean the oil from the surface, next,washing them in cool water to remove the solution and cool the gears sothat they will not heat the next bath, next, subjecting the gears to anelectrically operated acid bath, next, again washing the gears in coldwater, and then washing the gearsin a solution of sal soda (about oneound of sal soda to-ten or fifteengallons of water) to remove the acid.After drying, the ears are sometimes brushed with a fibre brus .toremove the slight deposit that is sometimes present on the surface andwhich may interfere with inspecting the gears.

The electrically operated acid bath above referred to is preferably asolution of approximately nine parts (by Volume) of water and one partof acid, the acid content consisting of two parts of commercial muriaticacid (specific gravity 1.15) and one part of commercial sulphuric acid(66 Baum). This acid bath should be kept cool in order to preventpitting of the gears and its acid content may be varied somewhat to suitthe particular case; Also; the length of time that the gears or otherarticles are subjected to this acid bath may be varied somewhat, theusual time-being from eight to twelve minutes. In a two hundred gallonlead lined tank ten carbon plates 10 "x 5"x 1% may be used and theelectrical connections are so made that these plates will operate as theanode and the work (that is the metal articles) as the cathode. Thistank when loaded may be run with say five volts to produce good results,and the amperage varies with the amount of work in the tank. Althoughthe invention or discovery has been described rather specifically as toparticular methods or processes that have been practiced under it, itwill be understood that it is not thus limited in its application.

Having thus described the invention or discovery, what is claimed as newand desired to be secured by Letters Patent is:

1. The process of treating hardened steel articles consisting in partlydrawing the temper from the article and then subjecting the article toan electrically operated acid bath to remove the scale.

2. The process of treating hardened steel articles consisting in partlydrawing the temper from the article, then cleaning the oil from thearticle, and then subjecting the article to an electrically operatedacid bath to remove the scale.

3. The process of treating hardened-steel articles consisting in partlydrawing the temper from the article, then subjecting the article to analkaline solution to clean the oil from the surface, and then subjectingthe article to an electrically operated acid bath to remove the scale.

4. The process of treating metal articles such as gears consisting inhardening the article as by heating and quenching, then heating thearticle to a lesser degree than when hardening to thus partly draw thetemper, and then subjecting the article to an electrically operated acidbath to remove the scale.

5. The process of treating metal articles consisting in heating thearticle and quenching in oil to harden it, then heating the article topartly draw the temper and cooling it, then subjecting the article to anoil cleaning bath, and then to an electrically operated acid bath toremove the scale.

In testimony whereof I aifix my signature.

WILLIAM H. GRAVES, JR.

